1. Field of the Invention
The present invention relates to electrical contactors and similar devices for completing and interrupting electrical current-carrying paths between a source of electrical energy and a load. More particularly, the invention relates to a coil assembly and actuator for such a device which facilitates assembly and installation, and which provides improved electrical, magnetic and thermal performance during transient and steady state phases of operation.
2. Description of the Related Art
A great variety of devices have been designed for completing and interrupting current-carrying paths between an electrical source and an electrical load. In one type of device, commonly referred to as a contactor, a set of movable contacts is displaced relative to a set of stationary contacts, so as to selectively complete a conductive path between the stationary contacts. In remote-controllable contactors of this type, an actuating assembly is provided to cause the movable contacts to shift between their open and closed positions. Such actuating assemblies typically include a coil forming an electromagnet, and a core to intensify a magnetic field generated around the coil when an actuating current is passed therethrough. The magnetic field attracts a movable armature which is coupled to the movable contacts within the device, thereby displacing the movable contacts and thus making electrical contact or closing the electrical circuit. When the actuating current is removed, biasing members return the movable assembly back to its normal position thus breaking the electrical connection or opening the electrical circuit.
Contactors of the type described above are commonly available with either alternating current or direct current actuating coil assemblies. The selection of either an alternating current assembly or a direct current assembly typically depends upon the type of electrical power available in the application. However, advantages and disadvantages are associated with each type of assembly. For example, direct current coils can be associated with simple solid core structures which do not need to minimize heating from circulating eddy currents found in alternating current coils. Also, direct current coils tend to have a higher force to power ratio because the current is steady and does not pass through zero with each half cycle as is the case with alternating current, and therefore require lower currents to obtain a desired armature pull-in or contact retaining force. Moreover, direct current assemblies do not require shading coils as are typically provided in alternating current assemblies, and therefore are quieter in operation and experience lower wear. On the other hand, alternating current power sources are very widespread and are favored in many cases due to their availability.
Coil assemblies for contactors have also been constructed with multiple coils, including coaxially aligned pickup coils and holding coils. Because a greater coil MMF is often required to close the contactor than is required during steady-state operation (i.e., after closure), both the pickup and holding coils are energized during closure, and with the pickup coil being deenergized following closure. The pickup coil is designed to have a significantly higher MMF and power than the hold coil. Turning off the pickup coil minimizes heating and reduces the power required once the armature has closed (i.e. steady state operation). Timing for deenergization of the pickup coil is typically fixed, and is set so as to provide sufficient force and time for displacement of the movable contact assembly to a closed position. However, if the time or force varies, as is sometimes the case, such arrangements may either provide insufficient or excessive periods of energization of the pickup coil. Also, such devices typically employ mechanical switches to release the pickup coil, or to switch the pickup coil in series with the holding coil following the initial closure period.
In addition to the foregoing drawbacks, where conventional coil assemblies are associated with control circuits supported on conventional circuit boards, these must often be supported by additional structures in the coil assembly or in the housing adjacent to the coil assembly. These structures add further to the cost of the device, and require additional labor for installation. Moreover, in multiple-coil actuating assemblies, care must be taken to ensure that proper polarity of the pickup and holding coils during electrical connection to the control circuit. Again, this can add to the cost of the device, and, in the event of an error in the polarity of the connections, can result in malfunction or the need to rework the assembly.
There is a need, therefore, for improved operator structures for contactors and similar electrical devices. In particular, there is a need for an actuating coil assembly in which multiple coils can be provided to reduce the power to the device during steady-state operation, but in which a pickup coil is energized for sufficient time to ensure adequate movement of the movable contact assembly. There is also a need for an improved coil structure which facilitates mounting of control circuit components and wiring of coil leads, thereby facilitating manufacturing of the overall assembly.